def calc_distance(p1, p2):
    from math import sqrt
    x1, y1 = p1
    x2, y2 = p2
    return sqrt((x2 - x1)**2 + (y2 - y1)**2)


if __name__ == '__main__':
    # ??????????????\???
    data = [float(x) for x in input().split(' ')]

    # 2???????????¢????¨????
    result = calc_distance((data[0], data[1]), (data[2], data[3]))

    # ???????????????
    print('{0:.8f}'.format(result)) def calc_distance(p1, p2):
    from math import sqrt
    x1, y1 = p1
    x2, y2 = p2
    return sqrt((x2 - x1)**2 + (y2 - y1)**2) calc_distance from math import sqrt x1, y1 = p1 x1 p1 y1 x2, y2 = p2 x2 p2 y2 return sqrt((x2 - x1)**2 + (y2 - y1)**2) sqrt((x2 - x1)**2 + (y2 - y1)**2) sqrt (x2 - x1)**2 + (y2 - y1)**2 (x2 - x1)**2 x2 - x1 x2 x1 2 (y2 - y1)**2 y2 - y1 y2 y1 2 p1 p1 p2 p2 if __name__ == '__main__':
    # ??????????????\???
    data = [float(x) for x in input().split(' ')]

    # 2???????????¢????¨????
    result = calc_distance((data[0], data[1]), (data[2], data[3]))

    # ???????????????
    print('{0:.8f}'.format(result)) __name__ == '__main__' __name__ '__main__' float(x) for x in input().split(' ') for x in input().split(' ') x input().split(' ') ().split () input split ' ' for x in input().split(' ') float(x) float x data = [float(x) for x in input().split(' ')] data [float(x) for x in input().split(' ')] result = calc_distance((data[0], data[1]), (data[2], data[3])) result calc_distance((data[0], data[1]), (data[2], data[3])) calc_distance (data[0], data[1]) data[0] data 0 data[1] data 1 (data[2], data[3]) data[2] data 2 data[3] data 3 print('{0:.8f}'.format(result)) print '{0:.8f}'.format(result) '{0:.8f}'.format '{0:.8f}' format result def calc_distance(p1, p2):
    from math import sqrt
    x1, y1 = p1
    x2, y2 = p2
    return sqrt((x2 - x1)**2 + (y2 - y1)**2) def calc_distance(p1, p2):
    from math import sqrt
    x1, y1 = p1
    x2, y2 = p2
    return sqrt((x2 - x1)**2 + (y2 - y1)**2) calc_distance result = calc_distance((data[0], data[1]), (data[2], data[3])) calc_distance((data[0], data[1]), (data[2], data[3])) result data = [float(x) for x in input().split(' ')] [float(x) for x in input().split(' ')] data
def calc_distance(p1, p2):
    from math import sqrt
    x1, y1 = p1
    x2, y2 = p2
    return sqrt((x2 - x1)**2 + (y2 - y1)**2)


if __name__ == '__main__':
    # ??????????????\???
    data = [float(x) for x in input().split(' ')]

    # 2???????????¢????¨????
    result = calc_distance((data[0], data[1]), (data[2], data[3]))

    # ???????????????
    print('{0:.8f}'.format(result))